Known folding machines cause various folds to occur during a series of successive exchanges between various cylinders whose axes are parallel.
First, the continuous web of paper is generally folded longitudinally by a folding component called a former board. The former board forms a continuous fold in the web running parallel to the two longitudinal edges of the web.
Next, this folded web of paper is cut transversely into copies between a cutting cylinder and a transfer cylinder. For this purpose, the cutting cylinder is equipped with external cutting blades arranged along the generatrices of the cylinder. The transfer cylinder includes a cylinder body provided, on its external surface, with impaling pins and corresponding rubber counterparts arranged along the generatrices of the transfer cylinder.
Thus, each set of impaling pins arranged in series along a generatrix of the transfer cylinder, and which project from the transfer cylinder, takes the web of paper as it runs off; the paper is then immediately cut transversely by means of a cutting blade coupled to the cutting cylinder pressing on the corresponding counterpart of the transfer cylinder.
Each copy thus cut is held by its front edge on the impaling pins projecting from the transfer cylinder. Then the copies receive a first transverse fold between the transfer cylinder and a folding cylinder. A transverse fold will be understood here to mean a fold perpendicular to the longitudinal edges of the copy.
In order to form this first fold, the transfer cylinder also includes, on its external surface, engaging blades arranged along generatrices of the transfer cylinder. The engaging blades are positioned at the external surface of the cylinder with a certain angular offset with respect to the position of the impaling pins. Thus, an engaging blade acts on each copy to be folded so as to introduce this copy into a folding jaw provided on the external surface of the folding cylinder along a generatrix.
It should be emphasized that a transfer cylinder will be understood to mean, on the one hand, a cylinder able to transport, over each set of impaling pins, a single copy so as to introduce it into a folding jaw, the transfer cylinder performing a half revolution between grasping the copy and introducing it into the folding jaw and, on the other hand, a cylinder able to transport, over each set of impaling pins, several copies simultaneously so as to introduce them into a folding jaw, the transfer cylinder then performing several revolutions so as to grasp several copies per set of impaling pins before introducing them into the folding jaw. Such a cylinder is commonly called, by a person skilled in the art, a "collecting transfer cylinder."
More particularly, the engaging blades are securely fastened to plates mounted pivotally on the body of the transfer cylinder. This makes it possible to modify the angular separation between the engaging blades and the impaling pins and hence to modify the position of the first transverse fold with respect to the front and rear edges of the copy.
Indeed, for a particular diameter of the transfer cylinder, in a first configuration, the engaging blades of the transfer cylinder are positioned at an angle of approximately 60.degree. with respect to the impaling pins so as to form a transverse fold in the middle of the length of each copy. In this case, the engaging blade acts in the middle of the copy to be folded, held by its front edge on the impaling pins so as to introduce it into the folding jaw. The impaling pins then retract and the folding cylinder takes the copy folded at its middle towards a square folding device or to a device for forming a second parallel fold.
In a second configuration, the engaging blades of the transfer cylinder are positioned at approximately 40 degrees to the rear with respect to the impaling pins which carry the copy, so as to form a transverse fold in the first third of the length of each copy. In this case, the engaging blade acts on the first third of the copy so as to introduce it into the folding jaw of the folding cylinder.
The mobile mounting of the engaging blades on the transfer cylinder is produced so that each engaging blade, mounted on the pivoting plates, is inserted in a housing provided in the body of the transfer cylinder, this housing being sufficiently wide to allow an angular deflection of the engaging blade at the external surface of the transfer cylinder. Thus, there exists in the majority of cases, a clearance between the engaging blade and the edges of the body of the transfer cylinder, which implies that the external transfer surface of a transfer cylinder may comprise empty spaces which correspond to the deflection clearances existing between the engaging blades and the body of the transfer cylinder. These spaces extend on either side of each engaging blade along the generatrices of the transfer cylinder.
These spaces on the external transfer surface are troublesome because, when a web of paper is flattened onto the transfer surface so as to be cut and folded, the edges of the web of paper may engage in spaces of the transfer surface and copies may then be obtained which are dog-eared or even torn on the edges.
In order to eliminate these spaces on the external transfer surface of the transfer cylinder and to obtain a globally continuous external surface, one known solution is to position a planar comb-shaped component on either side of each engaging blade, which component extends along a generatrix of the transfer cylinder and which is securely fastened to the respective engaging blade. The branches of each comb are inserted into opposite housings provided on the body of the cylinder which housings, in this place, also have the complementary shape of a comb. Thus, when the engaging blades are displaced angularly with respect to the impaling pins, the combs securely fastened to the engaging blades and extending on each side of the latter are at least substantially engaged in the combs securely fastened to the body of the cylinder in the region of the edges adjacent to the engaging blades.
This system of surface combs engaged in one another as a function of the angular separation between the engaging blades and the impaling pins is not satisfactory because the longitudinal edges of the web of paper can still pass, in an untoward fashion, into the free housings left between two successive branches of a comb and produce copies which are dog-eared or which have torn edges.